The technique disclosed in this specification relates to a cylinder head cover structure for an engine.
A typical cylinder head cover, placed over the top of a cylinder head of an engine, is provided with an oil separator on the interior of the cylinder head cover. (See, for example, Japanese Unexamined Patent Publication No. 2009-150289.) This oil separator includes an oil separating chamber for separating and removing oil mist contained in blow-by gas. An exterior wall of the cylinder head cover is provided with a positive crankcase ventilation (PCV) valve. The PCV valve releases the blow-by gas, from which the oil mist is separated and removed in the oil separating chamber, from the oil separating chamber to the intake system of the engine.
In cold weather, the valve body of the PCV valve could be less likely to operate smoothly because of frozen water contained in blow-by gas adhering to the PCV valve. Hence, in order to keep the PCV valve from freezing and facilitate defrosting of the PCV valve, the above publication discloses the following: an opening is provided on a separator plate acting as a partition wall between a blow-by chamber (the oil separating chamber) and a rocker housing (a cam housing), and a tip end of the PCV valve is projected through the opening into the rocker housing so that the tip end of the PCV valve is heated by the heat of lubricant oil splashing inside the rocker housing and the heat inside the rocker housing.